There are a lot of things that affect rasp. The shape of the cut, the depth of the cut, the number of tags left from the cut, the stagger of the reed stacks(overhang) and the material itself. Some colors seem to have more inherit rasp (red) than others (gray or natural).
This. There are many variables that affect the amount of rasp and the tone/pitch of a call. In fact, there are so many factors involved that it is pretty difficult to identify the combinations that consistently produce the most realistic sounds based on a given users abilities. Add to that the fact that very minute differences in call construction and the latex consistency can change the sound of any call significantly.
It should be noted that a mouth call user with lots of experience/skill can manipulate any decent call/cut design to produce both clear and raspy yelps just by changing air pressure and flow over the reeds. Air pressure is controlled primarily by diaphragm and throat tightening and tongue placement and pressure control air bursts over the reeds and the location of that air pressure over the reeds.
Master air and tongue control first and then learn how to modify each call to produce the sounds you are looking for.